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petrochemical
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petrochemical

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PETROCHEMICAL

chemical compound
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By The Editors of Encyclopaedia Britannica • Edit History

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Table of Contents
Grangemouth: petrochemical refinery
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petrochemical, in the strictest sense, any of a large group of chemicals (as
distinct from fuels) derived from petroleum and natural gas and used for a
variety of commercial purposes. The definition, however, has been broadened to
include the whole range of aliphatic, aromatic, and naphthenic organic
chemicals, as well as carbon black and such inorganic materials as sulfur and
ammonia. In many instances, a specific chemical included among the
petrochemicals may also be obtained from other sources, such as coal, coke, or
vegetable products. For example, materials such as benzene and naphthalene can
be made from either petroleum or coal, while ethyl alcohol may be of
petrochemical or vegetable origin. This makes it difficult to categorize a
specific substance as, strictly speaking, petrochemical or nonpetrochemical.

Products made from petrochemicals include such items as plastics, soaps and
detergents, solvents, drugs, fertilizers, pesticides, explosives, synthetic
fibres and rubbers, paints, epoxy resins, and flooring and insulating materials.
Petrochemicals are found in products as diverse as aspirin, luggage, boats,
automobiles, aircraft, polyester clothes, and recording discs and tapes.

Read More on This Topic
petroleum refining: Petrochemicals
By definition, petrochemicals are simply chemicals that happen to be derived
from a starting material obtained from petroleum....

Like crude oil and natural gas, petrochemicals are composed primarily of carbon
and hydrogen and are called hydrocarbons. If, in the molecules, the carbon atoms
are linked by single bonds, the molecules are said to be saturated. If they are
linked by one or more double bonds, the molecules are said to be unsaturated.
Unsaturated chemicals are preferred as petrochemical feedstocks because they are
more chemically reactive and can more easily be changed into other
petrochemicals.



The various components of petroleum used as raw materials in the production of
other chemicals are known as feedstocks. Petrochemical feedstocks can be
classified into three general groups: olefins, aromatics, and a third group that
includes synthesis gas and inorganics. Olefins, whose molecules form straight
chains and are unsaturated, include ethylene, propylene, and butadiene. Ethylene
is the hydrocarbon feedstock used in greatest volume in the petrochemical
industry. From ethylene, for example, are manufactured ethylene glycol, used in
polyester fibres and resins and in antifreezes; ethyl alcohol, a solvent and
chemical reagent; polyethylene, used in film and plastics; styrene, used in
resins, synthetic rubber, plastics, and polyesters; and ethylene dichloride, for
vinyl chloride, used in plastics and fibres. Propylene is used in making such
products as acrylics, rubbing alcohol, epoxy glue, and carpets. Butadiene is
used in making synthetic rubber, carpet fibres, paper coatings, and plastic
pipes.

Aromatics are hydrocarbon molecules that form rings and are unsaturated. The
major aromatic feedstocks are benzene, toluene, xylene, and naphthalene. Benzene
is used to make styrene, the basic ingredient of polystyrene plastics. It is
also used to make paints, epoxy resins, glues, and other adhesives. Toluene is
used primarily to make solvents, gasoline additives, and explosives. Xylene is
used in the manufacture of plastics and synthetic fibres and in the refining of
gasoline. Naphthalene is notably used in insecticides.

Synthesis gas is used to make ammonia and methanol. Ammonia is used primarily to
form ammonium nitrate, a source of fertilizer. Much of the methanol produced is
used in making formaldehyde. The rest is used to make polyester fibres,
plastics, and silicone rubber.

The petrochemical industry received its chief impetus in 1913 from the
development of the thermal-cracking process by which crude petroleum was
refined. The process yielded gaseous by-products that were at first used only as
illuminating gas or as fuel but were found useful as chemical raw materials in
the 1920s and ’30s. The introduction of catalytic cracking in 1937 and increased
supplies of natural gas brought further expansion of the industry.

This article was most recently revised and updated by Amy Tikkanen.



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some discrepancies. Please refer to the appropriate style manual or other
sources if you have any questions.
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Britannica, The Editors of Encyclopaedia. "petrochemical". Encyclopedia
Britannica, 28 Feb. 2020, https://www.britannica.com/science/petrochemical.
Accessed 14 April 2022.
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